kellogg



(No Model.) 3 Sheets-Sheet 3. M. G. KELLOGG.

MULTIPLE SWITGHBOARD.

Patented Oct. 26

raven/E7: 44/40 Q/faLoa 5 7a; MTMJJ,

IINTTnn STATES PATENT QFFICE,

MILO G. KELLOGG, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE KELLOGGSXVITCIIBOARD AND SUPPLY COMPANY, OF SAME PLACE.

M ULTIPLE SWITCHBOARD.

SPECIFICATION forming part of Letters Patent No.592/120, dated October26, 1897. Application filed February 12, 1895. Serial No. 538,137. (Nomodel.)

To all whom it may concern.-

Be it known that I, MILO G. KELLOGG, a citizen of the United States,residing in the city of Chicago, county of Cook, and State of Illinois,have invented certain new and useful Improvements in MultipleSwitchboards for Telephone-Exchanges, of which the following is a full,clear, concise, and exact description, reference being had to theaccompanying drawings, forming a part of this specification.

My invention relates to the telephone-exchange system described in myPatents No. 42%,310,dated March 25, 1890, and No. 427,087, dated May 6,1890, which system is generically known as the Divided exchange systemof multiple-switchboard operation.

It relates to certain improvements of said system adapting the same to ametallic-circuit telephone-exchange system.

Certain features of my invention, which I shall describe and claim, arealso applicable to metallic-circuit telephone-exchanges which are notoperated on the divided exchange system.

In the system which I shall herein describe the lines of the exchangeare divided into four classes or divisions, and the sections of multipleswitchboards are divided into four classes or divisions to correspond.Each line of one class is provided with a switch on each section ofboard of its class of boards and on one section of each of the otherclasses. Each line of the other classes is provided with a switch oneach section of board of its class of boards and on one section of eachof the other classes. For each line are four polarized annunciatorsplaced in the four classes of boards and at a section where the line hasa switch and its calls are to be answered. The annunciators should bepreferably distributed approximately equally among the sections of theclass of boards to which they belong. Two of the annunciators of eachline are con nected in opposite polarity in a normal ground connectionto one side or branch of the line, and the other two annunciators of theline are connected in opposite polarity in a normal ground connection tothe other side or branch of the line. A local circuit containing anelectromagnetic device is provided for each line with contacts by whichwhen the line is switched for conversation at either board said groundconnections which contain the annunciators of the line are automaticallyopened, and when the line is disconnected from the line with which it isswitched the normal ground connections through the annunciators areautomatically reestablished. The calling-generator at each subscribersstation has commutator devices and keys or switches, whereby thesubscriber may at will when the line is not switched, as hereinafterdescribed, send a current of either polarity from ground through eitherside or branch of the line to ground at the central office through thenormal ground connection which contains two of the polarizedannunciators, and thus be enabled at will to operate either one of hisfour annunciators and call an operator at either of the division ofboards and at a board where his line has a switch and it is intended hiscalls shall be attended to. Each operator has pairs of switching-plugs,with cords, and calling, answering, and clearing-out apparatus for thesame, by which she may at will connect with any line connected at theboard, answer their calls, connect the line with the line wanted, ringthe bell of the subscriber wanted, connect a clearing-out annunciator ina ground connection to one of the metallic circuits of his linesconnected together for conversation, and test any line to determinewhether or not it is switched for conversation. The local circuit ofeach line which automatically opens the normal ground connections of theline is also utilized for the test system, as will be explained indetail.

The invention which I shall herein illustrate and describe showsapparatus whereby two subscribers stations may be operated on onetelephone-line and each subscriber be enabled to call an operator ateither of the divisions of the board without signaling or disturbingeither of the other subscribers on his line, and the operator at theboard where the call is indicated may connect directly with thesubscriber who called and find out what other subscriber is wanted andconnect the calling-line directly with the line of the subscriberwanted. If the subscriber wanted by any other subscriber is one forwhich one line serves two subscribers, the operator in calling on thisline rings the bell of the subscriber wanted and not the bell of theother subscriber. Thus when either a subscriber or an operator calls ona line on which there are two subscribers stations the station wanted,whether it be the central-ofiice or a subscribers station, is promptlycalled, while there is no call indicated at either of the other stationsto attract unnecessary attention. While two subscribers can be servedwith one line, one may also be served by one line. One feature of thesystem is that both the subscribers and the operators of the exchangeperform substantially the same operations in obtaining and answeringcalls whether the line has one or two subscribers on it, and theseoperations are substantially the minimumin number and take substantiallythe smallest amount of time required in any telephone system to obtainconnection and service between two subscribers stations. Thefour-division exchange which I have outlined and which I shall describewill readily, in the present state of the art as to the construction ofswitches, annunciators, &c., provide switching facilities fortwenty-five thousand lines. serve for two subscribers. Thus fiftythousand-subscribers stations can be operated from one central stationwithout trunk-line connections between boards and the service obtainedbe as prompt and require substantially no more labor or expense perconnection than would be required in a little village exchange of onehundred subscribers, Where an operator makes the connections directlybetween one subscribers line and another. While two subscribers stationscan be served by one line, yet in very many cases the telephone businessof a subscriber is so great that true economy and good service requirean individual line for him. On the other hand, especially inresidence-districts, the subscriber uses his telephone but a few timeseach day and then but for a few minutes.

' In such cases two or more subscribers staand describe wouldaccommodate and give good and prompt exchange service to fromthirty-five to forty thousand subscribers stations located on thetwenty-five thousand lines. The system, moreover, as I shall alsoindicate, is adapted to give service with three or four subscribersstations on one line, as well as with one or two on a line. Thereforeone hundred thousand subscribers might be served from one exchangecenter, and giving such service as each might select, and about fiftythousand subscribers stations would stations on one line. Each line, asheretofore stated, can

probably be satisfactorily operated from one exchange center. Moreover,a divided exchange system is entirely feasible in which a greater numberof divisions than four may be used anda correspondingly greater numberof lines and subscribers could be accommodated thereby.

In the accompanying drawings, illustrating my invention, Figure 1-represents a front view of a section of one of the switchboards. Fig. 2shows a complete diagram of the mainline central-officeapparatus,circuits,and connections of the system with four classes ordivisions of boards to correspond with the four classes or divisions oflines and two lines connected thereto, one of each class A and O oflines and their central-office apparatus and connections. Fig. 3 showsin detail two subscribers-station apparatus to be used at twosubscribers stations on one line with the circuit connections betweenthem. Fig. 3" shows the connections of a subscribers-station apparatuswhere only one station is placed on a line. Fig. 3 shows a subscribersswitch which may be used with four subscribers Fig. 4: shows in diagraman operators cord system or apparatus to be used at the boards. Fig. 5shows in detail a polarized call-annunciator which may be used in thesystem. Fig. 6 shows an end view of the calling generator shaft of thesubscribers-station apparatus with two commutator-springs, one bearingon each side of the shaft. Fig. 4 shows a clearing-out annunciator whichmay be employed. Fig. 4: shows a modification of the clearing-outannunciator which may be used. Fig. 7 shows in detail a buzzer orelectromagnetic device which may be used at each subscribers station.Fig. 8 shows in detail a polarized call-bell which will respond to onlyone polarity of current and which may be used at the subscribersstation.

G in each case represents a ground connection. V

In Fig. 2, A A represent two boards of one class of boards; B 15*, twoboards of a second class of boards; 0 0 two boards of a third class ofboards, and D D two boards of the fourth class of boards. boards areindicated by the letters A, B, C, and D, respectively, to correspond.Each board is shown in a sectional View of a sec tion of its board, asindicated by the line (1 e in Fig. 1. As many sections or boards of eachclass or division of boards may be usedas is found necessary orconvenient for the number of operators required to answer the callswhich are made to that class of boards. convenience in designation Icall one class of lines Class A, a second class Class B, a third classClass O, and the fourth class Class D of lines to correspond with thedesignation of the different classes of board.

Each line of a class is indicated in the exchange catalogue or list andelsewhere by the letter or designation of its class-as, for in- For Thefour classes of stance, one line is designated 3%, another 365 a third376 anda fourth 4 The peculiar designation of the various classes boardsand lines and of thelines in each class is immaterial so long as thedivision is made and the distinction kept up. WVhere several subscribersstations are placed on one line, each line may have the designation asindicated above, while for the subscribers themselves numeralindications may be added. Thus if line 32 has four subscribers stationsthese stations may beindicated as liggAl, (3521\2, C 32;),77 32.54.77

Each line of one class-class A, for example-has a spring jack or switchof suitable character on each board of class A of boards and on oneboard of eachof the other classes. Each line of class B has a switch oneach board of class B of boards and on one board of each of the otherclasses. Each line of class C has a switch on each board of class C ofboards and 011 one board of each of the other classes. Each line ofclass D has a switch on each board of class D of boards and on one boardof each of the other classes.

The line swiches are marked S S. Each switch has two contact piecesmarked g j, with which, respectively, the two contactpieces of the loopswitch plugs shown in Fig. 4 and marked D D are connect-ed when a plugis placed into the switch for switching. These contact-pieces g j areconnected with themain-line circuit, as will hereinafter be described,and may therefore be called the main-line contacts of the switch.

Each switch has also three other contactpieces (marked a, h, and (1,)which are insulated from said other contact-pieces and are normally outof contact with each other; but when a switch'plug is inserted into aswitch it presses the contact-piece a into contact with b and (Z. \Vhenthe plugis withdrawn, the contact of a with b and (Z is automaticallybroken. The contacts a, b, and (Z are connected to the local system fordisconnecting the annunciators and for testing, as will be described,and may be called the local contacts of the switches. The last-mentionedcontact-piece d is at or extends to or near the front of the switch, sothat an operators test contact-piece may be readily connected to it fortesting.

Z- Z are the switch-holes, adapted to receive the plugs, and r r are therubber pieces, on which the metal parts are mounted.

The loop-switch plugs shown in Fig. 4 and adapted to be inserted intothe line-switches are of the shape substantially as shown, and each plughas two contact-pieces (marked on m.) \Vhen a plug is placed into aswitch, its contact 'm forms connection with the contact g of the switchand its contact m forms connection with the contact j of the switch,while the rubber insulation of the plug presses the piece a of theswitchinto contact with the pieces Z) and d.

The switches and plugs may be of the shape and construct-ionsubstantially as shown. They may, however, be greatly changed in shapeand construction and yet have substantially the same switch partsoperating in substantially the same manner or forming substantially thesame connections as heretofore described.

w w are the line polarized annunciators, of which there are four foreach line, one for each line being located in each division of boardsand at a board where the line has a switch and its calls are to beanswered.

00 :0 are the electromagnetic devices, of which there is one for eachline, constructed and arranged for the purpose of disconnecting the twosides of the line from its normal ground connection through thelineannunciators while the line is switched for conversation. Thisdevice consists, substantially, of an electromagnet and an armature forthe same with a retraetile spring and two pairs of contacts, (marked 0 cand c 0, respectively,) which are insulated from each other and areclosed when no current passes through the helix, but are automaticallybroken by the movement of the armature so as to be open while current ispassing through the helix. The electromagnetic deviceis, in fact, a backcontact relay with two pairs of insulated contacts.

The main-line connections are as follows and as shown: One side orbranch of the line is connected to one of the main-line contacts of eachof its switches on the several boardssay to contact g. It is alsoconnected to one of the insulated contacts of a pair-say of c cof theelectromagnetic device of the line. The other contact of c c is groundedthrough two of the polarized annunciators which are connected in thecircuit in opposite polarity. The other side or branch of the line isconnected to the other main-line contacts of its switches-sayj j-and isconnected to one of the contacts of the other pair of contacts" say 0cof the electromagnetic device, while the other contact of c c isgroundedthrough the two other polarized annunciators of the line, whichare also connected in their circuit in opposite polarities.

The local connections of the system are substantially as follows: All ofthe contacts a a of all the switches of the exchange are connectedtogether by a grounded circuit eonnection. One side of the battery B isconnected to this circuit connection. All of the contacts I) b of all ofthe switches of any given line are connected together and are alsoconnected to one side of the electromagnetic device a; of the line,while the other side of the electromagnetic device of the line isconnected to the other side of the battery B than that side which isconnected to the contacts a a of the switches. The contacts 05 d of theswitches of scribed.

IIO

ed therewith to show myinvention.

main-line circuits and connections are represented by solid lines andthe local circuits and connections are represented by broken lines.

Fig. 3 shows in diagram the apparatus fortwo subscribers stations on oneline with the apparatus, circuits, and connections connect- Theapparatus for the different stations are marked subscribers station 1and subscribers station 2. The apparatus at each station contains,substantially, the telephone-switch, (marked 1,) the subscriberstelephone, marked 2,) his signal-receivin g bell, (marked 3,) hiscalling-generator 4, a buzzer or nonpolarized signal-receiving device,(marked 5,) and four calling-keys, (marked 6 6 6 6.)

The telephone-switch 1 is a usual form of automatic switch, which closescertain contacts when the telephone is on the switch and opens them andcloses other contacts when the telephone is taken off the switch. Thetelephones are shown on the switches. That is their normal position, anda telephone is removed from the switch when it is desired to use it forconversation. The switch has a pair of contacts normally closed, butopen or responds when an intermittent current of one polarity passesthrough it, but does not sound or respond when the current of the otherpolarity passes through it.

The subscribers calling-generator 4 is a usual construction of telephonemagneto-calling generator modified as follows: There is an insulatedcontact-piece on the armatureshaft which is a half-circle and to whichone end of the armature-coil is connected. The remaining part of thecircle is an insulation, as shown in Fig. 6. There are two stationaryinsulated springs which bear on diametrically opposite parts of thatpart of the shaft of which the insulated piece is a part and which inthe movement of the armature alternately make and break connection withsaid insulated contact-piece. The contact'sprin gs are so placed inrelation to the armature that one of them is in contact with saidinsulated piece on the shaft when a current of one polarity is generatedin the coil and the other is in contact with it when a current of theother polarity is generated.

The buzzer device 5 (shown in greater detail in Fig. 7) is soconstructed that it will sound whenever intermittent currents of eitherpolarity pass through it. The use of this device will be'describedlater-when the operation of the system is described.

keys, each having one point on which the lever normally bears andanother point normally insulated from the lever and with which it comesinto contact when it is pressed or operated by the subscriber incalling.

The circuits of the subscribers-station apparatus, as shown in Fig. 3,are as follows: One side or branch of the metallic-circuit line passesto subscribers station 1 and thence passes successively through thenormally closed pair of contacts of two of its keys 6 6 A and B, foreXample-passing in each case to the key-lever first. It then passes inthe same manner through two of the keys 6 6 of the other station 2. Inlike manner the other side or branch of the line passes successivelythrough the normally closed pairs of contacts of the keys 0 D at each ofthe subscribers stations, passing in each case to the lever first.Thence one side or branch of the line passes successively through adifferent pair of the twonormally closed pairs of contacts of theswitches 1 1 at the two stations and thence to ground. Their circuitconnection back through the switch-contacts at the several stations andthence to ground are indicated by broken lines. In this circuitconnection are placed the two subscribers polarized signal-receivin gbells, on e at each station so connected in the circuit that one of themwill sound when an intermittent current of one polarity passes throughit and only then,

and the other will sound when an intermittent current of the otherpolarity passes through it and only then. One of the springcontacts ofthe subscribers generator is connected to the lower or normally opencontact of two of the keys 6 6, as A 0, one connected in each side orbranch of the line. The other spring of the generator is connected tothe two other contacts of the keys, as B D.

One side of the armature-coil of the generator is connected to theinsulated contactpiece on the armature-shaft. The other side of the coilis connected to the frame of the generator. The frame is connectedthrough the buzzer of the subscribers station and thence to a local wirebetween the two stations. This local wire then passes, by areturn-conductor, through the two other closed contacts of the twotelephone-switches 1 1 and thence to ground. This local wire is alsorepresented by broken lines and its use in connection with the systemwill hereinafter be described.

The pair of contacts of each telephoneswitch 1, which are normally openbut are closed when the telephone is removed from the switch, are in abridge connection between the two sides of the line, which bridgeconnection contains the subscribers tele phone.

' In Fig. 3 the connections of the subscrib- IIC . ers-station apparatusis shown when only one the other branch of the line and passingsuccessively through a third pair of normally closed contacts of each ofthe four switches and to ground. The drawings Figs. 3 and 3 being forapparatus adapted for use with one or two stations only on each line donot show the third pair of contacts. Fig. 3", however, shows'such aswitch. Its application to the system and the circuit connectionsthrough them, as described above, to provide for four subscribers on oneline will be apparcut to those skilled in the art.

In the operators cord apparatus shown in Fig. 4, D D are a pair ofloop-switch plugs, the construction and operation of which,when the sameare inserted into the line-switches, have heretofore been described. K KK K are four calling-keys, each with a keylever normally in contact withone contactpoint and out of contact with another contactpoint, and whena lever is depressed by the operator for signaling purposes it leavesits contact with one of the points and passes into contact with theother point. ".2 is the cleariugout annunciator,which maybenon-polarized, and should be of such construction as to oiterconsiderable resistance and retardation to telephone and similarcurrents. A retardation-coil may be used in the ground-circuit with theclearingout annunciator if found necessary or desirable. Y is alooping-in switch with two movable levers and two pairs of contacts onwhich the lever may be-alternately placed at the will of the operator. tis the operators telephone. a: is a retardation-coil for the operatorstelephone connected on one side to one side of the telephone, as shown,and on the other side to one side of a common test-battery B ,which isgrounded on the other side. B is an operators callinggeneratorsubstantially of the kind shown and described in Fig. 3, so as to giveat will current of either polarity. It should, however, preferably be apowergenerator. For each pair of plugs there are four calling-keys, alooping-in switch, and a clearing-out annunciator. One generator may beused for many operators. retardation-coil.

The connections of the operators cord apparatus are thus: Thecontactpiece m of each of the plugs is connected to its strand offlexible conductor,which is connected successively through the normallyclosed contacts of two Each operators telephone has its different keys,as K K and K K respectively, of the four keys, passing in each case tothe lever first, and they are afterward united, as shown. The two lowercontacts of keys K K are united by a circuit-conductor and are connectedto one of the insulated springs of the operators generator. In likemanner are the lower contacts of keys K K connected to the other springof the generator. The frame of the generator is connected to ground. Thecontacts 11?. m of the pair of plugs are united by a flexibleconductingcircuit. The two lovers of the switch Y are connected,respectively, to the two flexible conducting-circuits which unite thecontactpieces of the plugs.- The two sides of the operators telephoneare connected,respectively, to the two contact-pieces of a pair on whichthe switch-levers may at will be placed. That contact-piece of the otherpair which is made to form contact with the lever of the switch which isconnected to the circuit connection between m m of the plugs isconnected from between the keys K K and K K respectively,'through theclearing-out ann unciator o, and thence to ground.

It is evident from the apparatus as shown and described that theoperator may, by depressing the levers of K or K direct at willintermittent current of one or the other polarity to the circuits inwhich is one of the contacts m of the plugs and by depressing the leverof K or K direct at will intermittent current of one or the otherpolarity to the circuit in which is the other contact m. She may also,by operating the switch Y, connect her telephone in a bridge whichcontains her telephone and bridges across between the twoconductor-circuits which connect the contactpieces of the plugs. She mayalso, by placing the levers of the switch in the other position, groundthe cond noting-circuit which connects the contacts m m through theclearing-out annunciator o. The normal position of the switch Y shouldbe that in which the telephone bridges across between the two conductorsof the pair of plugs.

A retardation coil may be used in the ground connection with theclearing-out annunciator, if found necessary or desirable; also, anotherretardation-coil device may be used to ground the other cord-circuitorthat which connects the contacts m m of the pair of plugs, and in thiscase the retardation effect of the circuit in which is the clearing-outannunciator i) need not be so great. The clearing-out an n unciator 4:(shown in Fig. 4) has a pair of contacts which are automatically closedwhile the annunciator indicates a call, and thereby short-circuits theannunciator and any resistance which may be in circuit with it.

The side of the operators telephone which connects with the contacts m mof the plugs is connected through its retardation-coil and the battery13 to ground.

Each operator has as many pairs of plugs with their flexible cords andapparatus, as described, as she may need to make the necessaryconnections between subscribers. Their connections to the system will bethe same as that of the pair of plugs shown and such as will be apparentto those skilled in the art. The cords should'be long enough so that theoperator may connect with any switch at her board. The various partsshould be conveniently mounted for her work. Y

The side or branch of the line which contains the signal-receiving bellsof Fig. 3 should be connected to .the contact-springs g g of itsswitches, (shown in Fig. 2,) and of course the other side of the linewill then be connected to the contacts jj of its switches.

The operation of the system is as follows: When a subscriber wishes toconverse with any other subscriber, he finds out in the exchangelist orotherwise the designation or division to which the line belongs. He thenby pressing the proper key and operating his generator causes hisannunciator which is located at a board of the division to which theline wanted belongs to indicate a call. For instance, if the line Wantedbelongs to division A he would on calling press on his key A. I If itbelongs to division 13, he would press on key B; if to division 0 on key0, and if to division D on key D. If when he thus presses on one of hiskeys and operates his generator his line is not switched at the centraloffice and neither his own telephone nor the telephone of any othersubscriber on his line is switched for conversation, his generator is inclosed circuit with the annunciator located at the board wanted andcurrent will pass through the circuit of that polarity which willoperate the annunciator and attract the attention of the operator at theboard wanted. This closed circuit is from ground 'at the central officethrough the line-annunciator and the pair. of closed contacts of theline-relay to one side or branch of the line, thence to the subscribersstation, thence through the pair of contacts closed by pressing the key,thence through the subscribers generator, thence to the local-circuitconnection through the then-closed contacts of the automatic device ofthe generator, and thence successively through the closed pairs ofcontacts of the telephone-switches ofthe line to ground. The subscriberwill then takehis telephone from his switch, thus automaticallydisconnecting his line from the ground at its outer end and bridging histelephone between the two sides of the line, and the operator onnoticing the call on the annunciator will place one of her loop-plugsinto the switch of the line, its switch Y being then so that hertelephone bridges between the two sides of the line. The act of placingthe plug in the switch automatically disconnects the line from itsground connections through its annunciators, as will hereinafter bedescribed. The subscribers and the operators telephones are thus broughtinto closed circuit with each other, and the operator finds out whatline is wanted. She then tests the line wanted, as will hereinafter bedescribed, and if she finds that it is free or unswitched she places theother plug of the pair into the switch of this line. This act alsodisconnects this line from its ground connection through itsannunciators. She then presses on the key which is connected to thelast-mentioned plug, which is adapted to send current of the polarity tooperate the bell of the subscriber wanted, and the bell will be rung. Ifthere are two stations on the line, the bell at station 1 might beadapted to ring when current is directed through it by the pressing of Kand the bell at station 2 respond to the current of K When the bell ofthe subscriber wanted is rung, he also takes his telephone from itsswitch, thus connecting his telephone in a bridge between the two sidesof his line and disconnecting his line from its ground connection at itsouter end. The operator then moves his switch Y, so as to disconnect hertelephone from the circuit and ground the circuit through theclearing-out annunciator n. The two subscribers telephones being thus inclosed circuit with each other they carry on their conversation. Whenthey are through conversation, they place their telephones on theirswitches and one of them operates his calling-generator, pressing at thesame time on one of his calling-keys A or B. This brings the annunciatoro into a closed circuit with the generator, and the annunciator willindicate the clearing-out signal. This signal being thus given theoperator immediately removes the plugs from the switches. The lines arethereby automatically grounded again through their respectiveannunciators and are in their normal position ready to give or receivecalls.

When a line which has two or more subscribers on it is switched forconversation and one of them is using it, another subscriber on the linecannot give a signal at the central office on one of theline-annunciators, and thus cause confusion, for two reasons: First, theline is then disconnected from its ground connections throughitsannunciators, and, second, the generator is ungrounded at the outerend of the line from the opening of one of the normally closed pair ofcontacts of the switch of the subscriber who is already using the line.For the last reason the sub scriber on operating his generator will noteven cause the clearing-out annunciator to indicate a call. closed pairsof contacts of the telephoneswitches is especially to preventa falseclearing-out signal when a subscriber attempts to send a call while hisline is already in use by another subscriber.

When a subscriber operates his generator, as heretofore described, andthe same is in a closed circuit by reason of the line not being in use,his buzzer 5'will be in this closed circuit and will respond to thepulsations of the The use of the normally intermittent current. If,however, by reason of the line being already in use no closed circuit isestablished, there will be no sound from the buzzer. The subscriber willtherefore know when he operates his generator whether or not his line isalready in use, and if it should happen to be in use, which would butseldom be the case, he will wait until it is out of use, and then repeatthe operation of calling.

If four subscribers stations are placed on one line, as heretoforedescribed, instead of two, as shown in Fig. 3, the operator would havefour more keys for calling with each pair of plugs, and these keys wouldbe connected into the cord-circuit which connects the plug-contacts m mand to the other apparatus in the same way the keys shown in Fig. l areconnected to their cord-circuit and to the other apparatus. By means ofthese keys the operator could at will ring either of the four bellsconnected with each of the two lines to which the plugs are connected.Thus she would be able to call and connect for conversation any twosubscribers 011 any two lines of the exchange.

It is evident that three subscribers stations may be placed on one line,with their three call-bells connected, two in one branch and one in theother branch of the line, and that the operator may ring at will eitherof the three bells by pressing on her suitable calling'key. lVhenseveral subscribers stations are placed on one line, they will beselected so that they are located near each other, and as far aspossible so that they will require little or no telephone conversationwith each other. For this reason the circuit connections between themused for calling and indicated by broken lines in Fig. 3 will be shortconnections. For the same reason the subscribers of one line will veryseldom desire to carry on telephone conversation with each other. If,however, a subscriber should wish to carry on telephone conversationwith another subscriber located on the same line, he will place histelephone on its switch after giving his order at the central oflice,and the operator will then call the subscriber wanted by pressing on thesuitable calling-key. The rules of the exchange will provide that thesubscriber shall thus temporarily place his telephone on his switch whenhe desires c011- versation with another subscriber located on the sameline, and the operators may be in structed to remind him to do this whenhe makes a call for such a connection. The two subscribers will thentake their telephones from their switches, and the telephones willthereby be placed in closed circuit on their line. both will replacetheir telephones on the switches and the clearing-out signal willantomatically be indicated to the operator. By means of the operatorskeys with their levers connected to both plugs the operator can sendsignaling currents to the line from W hen their conversation iscompleted,.

which the call originated as well as to the other line. This arrangementis especially useful where the subscriber wan ted is located on the sameline as the calling subscriber.

It is evident that the system of calling to the central oiiice andclearing-out indication which I have herein described is also applicableto a threedivision or two-division system of the divided-exchangesystem. In that case one or two of the line-annunciators, as the casemight he, would be left out of the normally closed ground connections ofthe line and the corresponding calling keys omitted at the subscribersstations. \Vith a two-division system the two annunciators required forthe line might be polarized annunciators connected in a normally closedground connection to one side of the line, and in that case there wouldbe no normally closed ground connection to the other side of the line;or both ground connections might be used and one annuneiator placed ineach. In this case the annunciators need not be polarized. Again, thecalling and clearing-out system might be used in a straight ornon-divided exchange multiple system by omitting one of the normallyclosed ground connections at the central oflice and placing theline-annunciator in the other ground connection and e1nploying thesubscribers calling-keys adapted to operate it. In that case theline-annunciator need not be a polarized annunciator, and thecalling-generator may be such as to give alternate currents. Vhen thesystem which I have described is applied to telephoneexchanges whereonly one subscribers station is placed on each line, the operatorsgenerator may give alternate current and the subscribers bells may besuch as to respond to such currents.

The operation by which the normal ground connections of a line throughthe line-annunciators are automatically broken whenever a line isswitched at the central office is briefly this: lVhenever a plug isplaced in the switch of a line, it automatically closes the localcontacts a b of the switch, as heretofore described. This brings thebattery B and the electromagnetic device a: of the line into a closedlocal circuit, which causes the armature of the device to be attractedand opens the normally closed contacts connected with it. The closedlocal circuit may be traced thus: from the contact a of the switch toand through the battery B and thence through the helix of theelectromagnetic device to the contact I) of the switch. \Vhen the plugis removed, the contact between a and b is broken and the local circuitis therefore open.

The test system is as follows: When an operator desires to test any lineto determine whether or not it is switched at the central office, sheplaces the contact m of one of her switch-plugs on the contact-piece (Zof the switch of the line, the switch Y being then in position, so thather telephone bridges across the two cord-circuits of the plug. If theline is then switched for use, a closed circuit is established whichcontains the battery 13 and the operators telephone, and the operatorwill hear a click in her telephone and know that the line is already inuse. This closed circuit may be traced as follows: from the groundthrough the test-battery B and the retardation-coil and telephone of theoperator to the contact m of the plug used in testing, thence to thecontact 61 to which the plug is applied, and thence to the contact ofthe switch at which the line is switched, thence to contact a of thatswitch which is then in contact with d, and thence to ground through thecommon ground connection of the contacts a a of the switches of the eX-change. If the line is not switched at any board, no closed circuit willbe established on testing, because no contact cl of the line is incontact with its spring a. The operator will therefore hear no click inher telephone, and will thereby know that the line is not in use, andwill place a plug in its switch.

As heretofore indicated, the subscribers stations on any given line maybe indicated by the designations 1, 2, 3, and 4. The keys of theoperators may be marked 1, 2, 3, and 4, as heretofore indicated, and theapparatus of the exchange be so connected that the key marked 1 willring the bell at station 1, key 2 ring the bell at station 2, key 3 atstation 3,

. and key 4 at station 4. Thus the operators would always know what keyto depress to ring the bell of any particular subscriber.

As has been stated, the normal position of the switches Y, or theirposition when the pairs of plugs are left for future use after beingtaken from use, is such that the operators telephone is bridged acrossbetween the two conductors of the plugs. In that case the operator mayimmediately bring her telephone into connection with the callingsubscriber by merely inserting a plug into the switch of his line.Various expedients may be used to insure that the switches shall bebrought to their normal position, indicated above. For instance, themechanism of the switches may be made such that when the plugs arebrought down by their usual cordweights to their normal position theywill automatically move the switch to its normal position, or themechanism of the switches may be such that the plugs cannot take theirnormal positions until their switch Y is placed in its normal position.

ing-out annunciator indicates, and thereby prevent the operator who issending the signal from causing a continuous ring of one of the bells ofa subscriber on the other line connected with his. The short circuit ofthe annunciator-magnet which is then established may be traced from g tospring d, thence to point a, and through wire S to ground. The systemwhich has been heretofore described contemplates that the subscriberswhen sending the clearing-out signal shall always press on a special oneof their callingkeys,as,forinstance,keyA. Thesystemmay, however, bemodified-as, for instance, as shown in Fig. 4-so that the clearing-outannunciator will indicate a call when a connected subscriber operateshis generator and presses on either of' his four calling-keys. The twowires 0 p of Fig. 4 should be connected to the two sides of thecord-circuit, Fig. 4, to which they belong.

The calling system may also be modified in a manner similar to thatshown in my Patent No. 427,087, so that only three calling-keys need beused at each subscribers station to call the four divisions of boards.One division of board will then be called by operating the generatorwithout pressing on any calling-key. The connection of the clearing-outannunciator to the side of the circuit necessary to operate theclearing-out signal-when one key is dispensed with, as indicated above,

will be apparent to those skilled in the art.

The clearing-out annunciators may be connected permanently to theircord-circuits, as is preferred by some,instead of being switched fromtheir cord-circuit when the operators telephone is connected therewith,as shown in Fig. 4. Fig. 4 shows the clearing-out-annunciator connectionto the cord-circuit to be permanent.

The system by which the central office calls the desired subscriber isnot claimed herein, the same being covered by claims which I have madein another application filed by me.

I claim as my invention 1. In a telephone-exchange system,metallic-circuit lines divided into four classes, the switchboardsdivided into four classes, one class of boards for each class of lines,each line having a switch on each board of its class and on one board ofeach of the other classes, and switching apparatus whereby the operatorat any board may connect together any two lines which have theirswitches at her board, in combination with four polarized annunciatorsfor eachline, located at the four of said four annunciators, andelectromagnetic apparatus automatically controlled by the switching ofeach line to disconnect the line from its normal ground connectionsthrough its annunciators.

2. 111 a telephone exchange system, metallic-circuit lines divided intotwo classes, the switchboards divided into two classes, one class ofboards for each class of lines, each line having a switch on each boardof its class and on one board of the other class, and switchingapparatus whereby the operator at any board may connect together any twolines which have their switches at her board, in combination with twopolarized annunciators for each line, located at the two divisions ofboards and where the line has switches, through which annunciators connected in opposite polarity one side of the line is normally grounded,electric calling apparatus at each subscribers station to at will sendcurrent of either polarity through a ground-circuit containing said sideof the line to operate either of said two annunciators, andelectromagnetic apparatus automatically controlled by the switching ofeach line to dis connect the line from its normal ground connectionthrough its annunciators.

3. I11 a telephone-exehange system, metallic-circuit lines divided intotwo classes, the switchboards divided into two classes, one class ofboards for each class of lines, each line having a switch on each boardof its class and 011 one board of each of the other classes, andswitching apparatus whereby the operator at any board may connecttogether any two lines which have their switches at her board, incombination with two annunciators for each line, located at the twodivisions of boards, and where the line has switches, through one ofwhich annunciator-s one side of the line is normally grounded, andthrough the other one of which the other side of the line is normallygrounded, electric calling apparatus at each subscribers station to atwill send current through a ground-circuit containing each side of theline to operate either of said two annunciators,and electromagneticapparatus automatically controlled by the switching of each line todisconnect the line from its normal ground connections through itsannunciators.

i. In a telephone-exchange system, metallic-circuit lines, unconnectedwith the ground at the subscribers stations while in use forconversation, a switchboard, switches, one switch on said board for eachline, each switch having two contact-pieces to which respec-; tively thetwo sides of its line are connected,l and means at said board to connectany two lines into a metallic circuit for conversation by joining thetwo contact-pieces respectively of their switches,in combination with aground connection for each line between one of its two sides or branchesand the ground, and an an-: nunciator for each line located in its said;ground connection, electromagnetic appara-! tus for each lineautomatically operated by the switching of the line for conversation toopen said ground connection of its line, a callinggenerator at eachsubscribers station, and switching apparatus there to at the will of thesubscriber include the generator in a ground circuit with that branch ofthe line to which its said ground-circuit connection is normally made.

5. In a telephone-exchange system, metallic-circuit lines, and switchingapparatus at the central office to connect any two of said lines into aclosed metallic circuit for conversation, in combination with two groundconnections foreach line at the central office, one from each side orbranch of the line, a different line-annunciator in each of said twoground connections, and electromagnetic apparatus with a local circuitfor each line, including a battery, automatically operated by theswitching of the line for conversation to open its two said groundconnections, while the line is thus switched for conversation.

6. In a telephone-exchange system, a metallic-circuit telephone-line,one side or branch of which is normally grounded at the central office,a line-annunciator in its said ground connection, and switchingapparatus to connect said line for conversation, and then or while theline is thus connected, open its said ground connection, in combinationwith two substations to which the line extends, a signal-receivingground connection for said side or branch of said line at its outer end,the signal-receiving bells of the two substations in saidsignal-receiving ground connection, calling-generator apparatus at eachsubstation, and switching apparatus to at the will of the subscriberdisconnect said signal-receiving ground connection of the line and establish a grounded calling-circuit which includes said side or branch ofthe line and the line-annunciator, when the line is not thus switched,but does not include its said signal-receiving ground connection.

7. Two telephone-lines temporarily connected together at the centraloffice into a combined circuit for conversation and one of them havingtwo subscribersstations, at each of which is a signal-receiving bell,said receiving-bells being normally in a ground-circuit connection withthe line, in combination with a clearing-out annunciator at the centraloffice in a ground connection to said combined circuit and contacts toshort-circuit said annunciator, or ground the combined circuit through acircuit of comparatively no resistance, while the annunciator indicatesa call, whereby either of said signal-receiving bells of said line willbe short-circuited so as to prevent them from sounding continuously whena clearing-out signal is sent from the other line.

8. Two telephone-lines temporarily connected togetherat the centraloffice into a combined circuit for conversation, and one of them havingtwo subscribers stations, a1

each of which is a signal-receiving bell, said bells being each normallyin a circuit with the line, in combination with a clearing-outannunciator at the central ottice in connection with said combinedcircuits, and with contacts to short-circuit said signal-receiving bellswhenever the annunciator indicates a call, whereby a clearing-out signalsent from the other line will not cause either of said signal-receivingbells to give a prolonged signal.

9. In a divided central exchange, annunciators, one at each division ofthe exchange for each line, each normally or as long as the line is notswitched at the central office in a circuit connection connected withthe line, a relay in a relay-circuit for all of said aununciators ofeach line, opening the circuit of the annunciators connected with theline, and an operators switch for putting said relay into action.

10. In a divided central exchange, annunciators, one at each division ofthe exchange for each line, each normally or as long as the line is notswitched at the central oftice in a circuit connection connected withthe line, a relay in a relay-circuit for all of said annunciators ofeach line, opening the circuit of the annunciators connected with theline, put into action by the act of switching said line for use.

11. In a divided central party line exchange, annunciators, one at eachdivision of the exchange for each line, means for rendering saidannunciators irresponsive to calling-currents from the subscribersstations, while the lines are switched for conversavtion, in combinationwith signal-receiving bells at the several subscribers stations of eachline and means for making them irresponsive to the samecalling-currents.

12. In a telephone-exchange system, a metalliccircuit telephone-line,one side or branch of which is normally grounded at the central-office,a line-annunciatorwin its said ground connection and switching apparatusto connect said line for conversation, and then or while the line isthus connected, making said annunciator inoperative to calls over theline, in combination with two substations to which the line extends,asignal-receivin g ground connection for said side or branch of saidline at its outer end, the signal-receiving bells of the two substationsin said signal-receiving ground connection, calling-generator apparatusat each substation, and switching apparatus to at the will of thesubscriber disconnect said signal-receiving ground connection of theline and establish a grounded calling-circuit which includes said sideor branch of the line and the lineannunciator, when the line is not thusswitched, but does not include its said signal-receiving groundconnection.

13. In a telephone-exchange system, atelephone-line normally grounded atthe central office, and a line annunciator in its said groundconnection, in combination with two substations to which the lineextends, a subscribers calling-generator at each of the substations, asubscribers calling-key at each of the substations operated at the willof the subscriber, each key having a line-contact connected with ,theline and another or ground-contact normally insulated from saidline-contact but connected with the line-contact when the key isoperated by the subscriber, said ground-contact of each key beingconnected to one side of the subscribers generator at its substation,the other sides of the two subscribers generators being brought to acommon connection which extends to the two substations and thence toground, and two telephone-switches, one at each substation, each havinga pair of contacts normally closed but open while the telephone isswitched for use, said common connection which extends to the twosubstations and thence to ground passing successively in series throughsaid pair of normally closed contact-points, of each of saidtelephone-switches, substantially as and for the purpose set forth.

14. In a telephone-exchange system, a telephone-line normally groundedat the central ofifice and a line annunciator in its said groundconnection in combination with two substations to which the lineextends, a subscribers calling-generator at each of the substations, asubscribers calling-keyat each of the substations operated at the willof the subscriber, a signal-receiving bell at one of the substationseach key having a pair of normally closed contacts through which pairsof contacts of the two keys the line normally passes and thence toground through said signal-receiving bell, said pair of contacts beingopened when the key is operated each key having a third or groundcontact normally insulated its two other contacts and into which thatone of them which is then connected with the line is brought intocontact when the key is operated, said third or ground contact of eachkey being connected to one side of the subscribers generator at itssubstation, the other sides of the two substations being brought to acommon connection which extends to the two substations and thence toground, and two telephoneswitches, one at each station, each having apair of contacts normally closed but open while the telephone isswitched for use, said common connection which extends to the two erscalling-generator at each of the substations, a subscribers calling-keyat each of the substations operated at the will of the subscriber, eachkey having a line-contact connected with the line and another or returncontact normally insulated from said line-contact but connected with theline-contact when the key is operated by the subscriber, saidreturn-contact of each key being connected to one side of thesubscribers generator at its substation, the other sides of the twosubscribers generators being brought to a common connection whichextends to the two substations and thence to said return,

and two telephone-switehes, one at each substation each having a pair ofcontacts normally closed but open while the telephone is switched foruse, said common connection which extends to the two substations andthence to said return passing successively in series through said pairof normally closed contact-points of each of said telephoneswitches,substantially as and for the purpose set forth.

16. In a telephone-exchange system, a tele phone-line normally connectedto a return at the central otlice and a line-annunciator in itsconnection in combination with two substations to which the lineextends, a subscribers calling-generator at each of the substations, asubscribers calling-key at each of the substations, operated at the willof the subscriber, a signal-receiving bell at one of the substationseach key having a pair of normally closed contacts through which pairsof contacts of the two keys the line normally passes and thence toground through said signal-receiving bell, said pair of contacts beingopened when the key is operated each key havin g a third or returncontact normally insulated its two other contacts and into which thatone of them which is then connected with the line is brought intocontact when the key is operated, said third or return contact of eachkey being connected to one side of the subscribers generator at itssubstation, the other sides of the two substations being brought to acommon connection which extends to the two substations and thence tosaid return, and two telephone-switchcs, one at each substation, eachhaving a pair of contacts normally closed but open while the telephoneis switched for use said common connection, which extends to the twosubstations and thence to said ground passing successively in seriesthrough said pair of normally closed contact-points of each of saidtelephone-switches, substantially as and for the purpose set forth.

In testimony whereof I have hereunto subscribed my name.

MILO G. KELLOGG.

Witnesses:

II. M. WALKER, E. S. WALKER.

